Do I need trailing arms on my custom IRS chassis?

[onevoice]

Originally Posted by bdahlg68

I think the OP was mainly concerned with function, and not whether or not this was the optimum IRS style. It will work without toe links. Yes, most other IRS's have a toe link, but there are not many "swing arm" style IRS's out there, but there are some good ones. Check out the previous BMW X5 rear suspension for instance. Quite different from the OP's suspension and does have two upper links, but not really a toe link. Nor are the upper links all that effective at completely limiting roll / twist as they have rubber bushings.

Not sure what you are getting at here. I wasn't talking about toe links. I said all IRS suspensions control the fore and aft movement of the upper part of the spindle from the top , think constraint of caster. All IRS suspensions also control the toe, whether with a toe link(like a vette or viper), or the physical layout of the locating arms like this design.

From the side view, the spindle as designed only resists rotation from the lower control arm. This is no way to design a performance suspension, unless the lower arm is super strong, because the forces will constantly be twisting the lower arm.

This design would be much better by spreading the upper link inner attaching point into two pieces, making it an A-arm. Same effect by using an upper trailing link.

Also, I'm not a big fan of modifying such a critical part as a spindle to use the steering arm location mounts as lower suspension mounts. Without obvious overkill design, it is foolish to do so without engineering analysis by someone familiar with the design and strengths of the original part.